1. Field of the Invention
There are many situations where it is desirable to have a highly concentrated aqueous solution of a sparingly soluble inorganic salt. Such solutions find particular application where a metered addition of the inorganic salt is required within relatively narrow concentration limits, the metered solution being used directly or diluted. An excellent illustration of this situation is a hemodialysis system, where it is desirable to ship the preformed salt solutions at high concentration to minimize the cost of handling and shipment. The hemodialysis unit can then monitor the dilution of the concentrate to provide the necessary salt concentration in the dialysis unit. Other situations where supersaturated aqueous solutions might find use are carbonates in fire extinguishers, preparation of crystals of enhanced size, and in chemical reactions.
Enhanced concentrations of sodium bicarbonate, beyond the solubility limits at ambient temperatures, are of particular interest for hemodialysis. While bicarbonate has always been recognized as the normal physiologic buffer-anion for control of blood pH, its utilization as a component of dialysate in extracorporeal hemodialysis has been confounded by solubility problems peculiar to aqueous solutions of sodium bicarbonate containing other electrolytes required to maintain isotonicity with blood plasma and by the instability of dissolved bicarbonate to changes in pH and carbon dioxide tension. There has therefore been substantial efforts in this field to develop concentrate solutions which can find acceptance in a hemodialysis unit, while providing the desired high concentration for preparation and shipment.
2. Brief Description of the Prior Art
Van Wager, J. R., "Phosphorus and Its Compounds," Vol. II, Interscience Publishers, New York (1961) gives a general description of utilities for polyphosphates.